They don't create that much drag - not enough to make any sort of significant difference. If it's creating drag, maybe it's stretched?

I agree with Lena's points - it does make a difference when watching the game - it's definitely helpful for spectators.

I'm in two minds about the vests - I can see the benefits but I can also see the reasons some hate them.

I think the rule is that 80% of the torso needs to be covered, is that right?